The present invention relates to a method and apparatus for applying charged particle beams and, particularly, to a technology effectively applied to a high-speed and high-accuracy apparatus for applying charged particle beams, which is used for semiconductor manufacturing devices and semiconductor inspection apparatuses.
Examples of technologies studied by the present inventors are as follows in a charged electron beam applied technology for use in a semiconductor manufacturing process.
In the semiconductor manufacturing process, an electron beam lithography system is used for drawing a desired circuit pattern on a wafer or mask as a subject. Also, electron microscopes, electron-beam inspection devices, and other devices are used for irradiating the subject with electron beams and checking, from signals of secondary electrons or the like produced, the shape of a pattern formed on the subject or the presence or absence of a defect of the pattern.
In these semiconductor manufacturing devices applying electron beams, it is an important problem that the speed of processing the subject, i.e., throughput is improved along with accuracy. To solve this problem, in Japanese Patent Laid-Open Publication No. 2001-267221 and Japanese Patent Laid-Open Publication No. 2002-319532, for example, there is proposed a multibeam method in which: a test sample is irradiated with a plurality of electron beams; these electron beams are deflected for scanning on the test sample; and, depending on the pattern to be drawn, the plurality of electron beams are individually turned on/off to draw the pattern. One example of such an electron beam lithography system of this type is described by using a schematic drawing of FIG. 13.
In FIG. 13, a one-dot-chain line represents a beam axis, which is an axis on which axes of symmetry of an electron gun and an electromagnetic lens formed in approximately rotation symmetry should coincide with each other, the beam axis serving as a reference of a beam path.
In this example, a thermal electron gun obtaining easily a large current and stable in electron emission is used. The thermal electron gun heats a cathode 101 made of a material with a low work function to provide electrons with energy enough to overcome a barrier of a cathode surface, and accelerates the electrons toward an anode 103 with a higher potential with respect to the cathode 101. The reference numeral “104” denotes a crossover of electron beams. The “crossover” is an image formed when electron beams emitted in the same direction from different positions in the same cathode cross one another. The size (diameter) of the crossover is called a crossover diameter, and a position where the crossover is formed on the beam axis is called a crossover height.
A source forming lens 105 is an electromagnetic lens having a function of forming an image by reducing the crossover 104. That is, a first intermediate image of the crossover 104 is formed. Herein, since the crossover is used as a light source, it is called a source crossover 106.
Note that as shown in FIG. 14, the electron beams emitted from the electron gun may be incident on the source forming lens 105 without forming a crossover. Also in this case, if a track of the electron beams is extrapolated linearly from a side of the source forming lens and a point 104b crossing on the beam axis is virtually handled as a crossover, this situation is similar to that as described above. Therefore, the point 104b is referred to as a virtual crossover.
By using this source crossover 106 as a light source, a condenser lens 107 produces an approximately parallel electron beam. The condenser lens 107 is an electromagnetic lens. The reference numeral “108” represents an aperture array formed by two-dimensionally arranging apertures. “109” a lens array formed by two-dimensionally arranging electrostatic lenses having the same focal length. “110” and “111” each a deflector array formed by two-dimensionally arranging electrostatic deflectors capable of being driven individually. “112” a blanker array formed by two-dimensionally arranging electrostatic blankers capable of being driven individually.
The approximately parallel electron beam produced by condenser lens 107 is divided by the aperture array 108 into a plurality of electron beams. The divided electron beams are converged at the height of the blanker array 112 by lens action of the corresponding lens array 109. That is, a second intermediate image of the crossover is formed. At this time, the deflector arrays 110 and 111 individually adjust paths of respective electron beams so that the corresponding beams pass through desired positions in the corresponding blankers.
The blanker array 112 controls whether the test sample is irradiated with the corresponding electron beam. That is, the electron beams deflected by the blankers are intercepted by a blanking aperture 114, and does not reach onto the test sample. On the other hand, the beams not deflected by the blanker pass through the blanking aperture 114 to reach onto the test sample 119.
Reducing glasses 113 and 115 and objective lenses 116 and 118 project, on a test sample 119 mounted on a stage 120, the reduced second intermediate image of the crossover formed at the height of the blanker array 112. The position of the reduced projected image is determined depending on a deflection amount by a deflector 117.